56 The Role of Dynamic Stabilization and the Aging Spine
Devices
Interspinous Spacers
X-Stop (Kyphon)
X-Stop is a titanium alloy device that is designed to stop extension (Figure 56-1). The oval spacer conforms to the interspinous space, and the wings prevent lateral migration. It is minimally invasive and inserted laterally, thus preserving the supraspinous ligament. It is designed to be implanted under local anesthesia. In clinical trial, X-Stop was significantly better than nonoperative treatment of lumbar spinal stenosis at 1 and 2 years post-op. The observed success rate was comparable to published reports for decompressive laminectomy, but with considerably lower morbidity.1,5 X-Stop is currently approved by the U.S. Food and Drug Administration (FDA) for use in patients with claudication symptoms from lumbar stenosis. Patients with relief in flexion and who are otherwise comfortable sitting respond well.
Wallis (Zimmer Spine)
The Wallis device is a PEEK interspinous spacer secured to the spinous processes using PET bands (Figure 56-2). It is designed to block extension and control flexion. Indications include isolated lumbar intervertebral instability, such as herniated discs, Modic I degenerative lesions, degenerative disc disease at a level adjacent to a previous fusion, and spinal stenosis treated without laminectomy. In long term (13 year) OUS follow-up, the device obviated the need for arthrodesis in 80% of patients.4 The Wallis device is currently undergoing clinical evaluation and is not FDA approved.
Diam (Medtronic)
Diam is an interspinous stabilizer composed of a silicone bumper, encased in polyester mesh, and secured with polyester sutures (Figure 56-3). It is inserted with minimal access and minimal tissue disruption. It is designed to resist extension and reduce intradiscal pressure. Indications include restoration of early segmental degeneration, correction of misalignment often seen in discectomy, and stenosis. Diam is currently undergoing clinical evaluation and is not FDA approved.
Coflex (Paradigm)
Coflex is a titanium alloy device whose U-shaped body conforms to the interspinous and interlaminar space (Figure 56-4). It acts as a stiff spring, dynamically stabilizing extension. Lateral migration is prevented by wings compressed onto the spinous processes. Indications include lumbar stenosis, adjacent segment disease, recurrent HNP and early symptomatic disc degeneration. In OUS implantation after decompressive laminectomy in degenerative lumbar spinal stenosis, Coflex was found to be less invasive and provided similar clinical outcome in comparison with instrumented fusion.2 Coflex is currently undergoing clinical evaluation and is not FDA approved.
ExtenSure (NuVasive)
ExtenSure is a PEEK interspinous spacer secured by geometric conformity to the anatomy and the suturing of the supraspinous ligament (Figure 56-5). It is designed to alleviate pseudoclauditory symptoms and radicular symptoms by enlarging the central canal, lateral recess, and foramina. It also decreases or eliminates low back pain by decreasing pressure on arthritic facet joints, degenerative discs, or both. It also restores disc height and foraminal volume. It is indicated in moderate to severe spinal stenosis, degenerative spondylolisthesis, and mild to moderate degenerative scoliosis. ExtenSure is currently undergoing clinical evaluation and is not FDA approved.
In-Space (Synthes)
In-Space is a laterally placed PEEK cylindrical device, secured by deployable wings (Figure 56-6). It is intended to stop segmental extension and to distract the symptomatic interspinous space. In doing so, maintenance of foraminal height, opening of the area of the spinal canal, reduction of stress on the facets, and relieving of pressure on the posterior annulus results. It is indicated in lumbar spinal stenosis, disc protrusions with discogenic low back pain, facet syndrome due to face osteoarthritis, degenerative spondylolisthesis up to grade 1, and degenerative disc disease. In-Space is not FDA approved.
Superion (Vertiflex)
Superion is a titanium alloy interspinous device with deployable wings (Figure 56-7). It is designed for percutaneous implantation in the treatment of moderate degenerative lumbar stenosis at one or two levels. Superion is currently under clinical investigation in the United States and is not FDA approved.